Method for forming steep spacer in a MOS device

ABSTRACT

Steep spacer is formed by using depositing and etching of dual conformal layers. A first conformal dielectric layer is deposited on a substrate with a gate electrode structure formed thereon. Then, a second conformal layer is deposited on the first conformal dielectric layer. The second conformal layer is anisotropically etched to form a first spacer on the sidewall of the first conformal dielectric layer. Next, the first conformal layer is anisotropically etched by using the first spacer as a mask to form a second spacer on the sidewall of the gate electrode structure. Then, the first spacer is removed and the second spacer is steep.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a method for forming a spacer in a MOS (metal-oxide-semiconductor) device, and more particularly to a method for fabricating steep spacer in a MOS device.

[0003] 2. Description of the Prior Art

[0004] Spacer plays an important role in hot carrier immunity of the MOS device. Spacer in a MOS device is formed by anisotropically etching a conformal dielectric layer, such as TEOS (tetra-ethyl-orthosilicate) or silicon nitride. FIG. 1 shows a standard, conventional MOS device, or MOS transistor. A substrate 100 with source/drain 110 formed therein is provided. Field isolation region 120, such as FOX (Field Oxidation), is formed on the substrate such that active area is among field isolation region 120. A gate electrode structure, including a gate dielectric layer 122 and a poly gate layer 124, is formed on the substrate 100. Spacer 130 is then formed on the sidewall of the gate electrode structure. Source/drain region 110 is then formed by ion-implantation.

[0005] In general, the shape of spacer is not steep enough. The oblique spacer 130 is easy to bridge the source/drain region 110 with gate electrode in salicide (self-aligned silicide) process. FIG. 2 is a case of showing a result of bridge between gate electrode and source/drain region 110 in a salicide process. A salicide layer 142, such as titanium salicide or cobalt salicide, is formed by depositing a metal layer, titanium or cobalt respectively, on the substrate 100 and performing a RTA (rapid thermal anneal) process. Metal layer will react will poly gate 124 and silicon on source/drain 110 to form silicide layer 142.

[0006] However, if metal layer is deposited excessively, there may be undue metal between gate and source/drain region 110 to conduct gate and source/drain region 110. This is usually occurred when spacer 130 is oblique, or the device dimension is scaled down. Therefore, this issue must be solved.

SUMMARY OF THE INVENTION

[0007] In accordance with the present invention, it is a main object of this invention to form steep spacer in a MOS device that substantially prevents S/D and gate bridging.

[0008] It is another object of this invention that steep spacer is very desirable in the salicide process as the device dimension scaled down.

[0009] In one embodiment, a method for forming a steep spacer in a metal-oxide-semiconductor device is disclosed. The method includes a first step of depositing a first conformal dielectric layer on a substrate having a gate electrode structure formed thereon. A gate electrode structure, including a gate dielectric layer and a poly gate layer. The first conformal dielectric layer may be TEOS or silicon nitride. Then, a second conformal dummy layer is deposited on the first conformal dielectric layer. During etching, the second conformal dummy layer must have different selectivity to the first conformal dielectric layer. Next, the second conformal dummy layer is anisotropically etched to form a first spacer on sidewall of the first conformal dielectric layer, and the first conformal dielectric layer is then anisotropically etched by using the first spacer as a mask to form a second spacer on sidewall of the gate electrode structure. The first spacer is removed and the second spacer is therefore steep.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

[0011]FIG. 1 shows a cross-sectional view of a substrate having a conventional MOS transistor formed therein and thereon between field isolation regions;

[0012]FIG. 2 shows the substrate of FIG. 1 after salicide process with the silicide layer formed thereon;

[0013]FIG. 3 shows a cross-sectional view of a substrate having two conformal layers formed on a gate electrode in accordance with a currently preferred embodiment;

[0014]FIG. 4 shows the substrate of FIG. 3 after anisotropically etching the first conformal layer to form a first spacer in accordance with a currently preferred embodiment;

[0015]FIG. 5 shows the substrate of FIG. 4 after anisotropically etching the second conformal layer by using the first spacer as a mask to form a second spacer in accordance with a currently preferred embodiment; and

[0016]FIG. 6 shows the substrate of FIG. 5 after removing the first spacer in accordance with a currently preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] Some sample embodiments of the invention will now be described in greater detail. Nevertheless, it should be recognized that the present invention can be practiced in a wide range of other embodiments besides those explicitly described, and the scope of the present invention is expressly not limited except as specified in the accompanying claims.

[0018] Moreover, while the present invention is illustrated by a number of preferred embodiments directed to silicon semiconductor devices, it is not intended that these illustrations be a limitation on the scope or applicability of the present invention. Further, while the illustrative examples use insulated gate control structures, it should be recognized that the insulated gate portions may be replaced with light activated or current activated structure(s). Thus, it is not intended that the semiconductor devices of the present invention be limited to the structures illustrated. These devices are included to demonstrate the utility and application of the present invention to presently preferred embodiments.

[0019] Further, various parts of the semiconductor elements have not been drawn to scale. Certain dimensions have been exaggerated in relation to other dimensions in order to provide a clearer illustration and understanding of the present invention. Enhancement and depletion mode structures may be similarly interchanged.

[0020] Further, although the embodiments illustrated herein are shown in two dimensional views with various regions having width and depth, it should be clearly understood that these regions are illustrations of only a portion of a single cell of a device, which may include a plurality of such cells arranged in a three-dimensional structure. Accordingly, these regions will have three dimensions, including length, width and depth, when fabricated in an actual device.

[0021] The present invention substantially adds a dummy conformal layer and an etching step to form steep spacer, and this dummy layer can be polysilicon layer, silicon nitride layer, or any other material that has different etching selectivity to material of the steep spacer.

[0022] The main steps of this invention are disclosed below and the first step is to deposit a first conformal dielectric layer on a substrate with a gate electrode formed thereon. As key steps in this invention, a second conformal dummy layer is deposited on the first conformal dielectric layer, and the second conformal dummy layer is then anisotropically etched to form a first spacer on sidewall of dielectric layer. Next, the first conformal dielectric layer is then anisotropically etched to form a steep spacer on side wall of gate electrode by using the first spacer as a mask, and the first spacer is then removed. Suitable conditions for performing various steps set forth above are set forth below and will be explained by reference to FIG. 3 to FIG. 6.

[0023] Referring to FIG. 3, a substrate 10 is shown wherein an active area is isolated by isolation regions 20. The isolation regions 20 in this embodiment are FOX (field oxidation) formed by LOCOS (local oxidation) process, and shallow trench isolation may also be used here. The active area includes a gate electrode, which has a polysilicon layer 24 formed on a silicon oxide layer 22, and two implanted wells 12 in the substrate 10. The two wells 12 in this embodiment are LDD (lightly-doped drain), and formed after the formation of gate electrode by using ion-implantation process.

[0024] The following step is to deposit a conformal dielectric layer 26 of thickness between about 500 angstroms to about 3000 angstroms on the substrate 10. The layer 26 is covered polysilicon layer 24, implanted wells 12, isolation regions 20. Material of this dielectric layer 26 is usually TEOS formed by conventional CVD (chemical vapor deposition) method. However, silicon nitride is another common material used for spacer, and this dielectric layer 26 is silicon nitride formed by using LPCVD (low pressure chemical vapor deposition) method. In this embodiment, TEOS layer is preferred as the conformal dielectric layer 26.

[0025] As a key step of this invention, a first conformal dummy layer 28 of thickness between about 100 to 200 angstroms is sequentially deposited on the dielectric layer 26. Material of this conformal dummy layer 28 must have different etching selectivity to the dielectric layer 26. The etching speed is dummy layer 28 faster then dielectric layer 26. If the dielectric layer 26 is silicon nitride, this conformal dummy layer 28 may be silicon oxide. In this embodiment, the dielectric layer 26 is TEOS, and the conformal dummy layer 28 may be silicon nitride or polysilicon. However, polysilicon is preferred, and may be formed by using any conventional LPCVD method.

[0026] Referring to FIG. 4, as another key step of this invention, the conformal dummy layer 28 is anisotropically etched to form a first spacer 29 on sidewall of the dielectric layer 26 adjacent to the gate electrode. Because this anisotropically etching step will etch the thickness of deposited conformal dummy layer 28, conformal dummy layer 28 on the sidewall of dielectric layer 26 is thicker than other place, and will not increased any reaction parameter in the process, and will not be removed after etching process. In this embodiment, we used by anisotropically etching method.

[0027] Referring to FIG. 5, to proceed the second etching form a steep second spacer 30, the first spacer 29 as a mask can protected second spacer shape, prevents from etching a portion of dielectric layer 26 adjacent to sidewall of the gate electrode. In this embodiment, we used by anisotropically etching method.

[0028] Referring to FIG. 6, the second spacer 30 obtain from second etching process, and the first spacer 29 is cover on the second spacer 30, the first spacer 29 was dipped off by the solution in the step of pre-metal cleaning using any conventional method for heavy doping of source and drain. We can obtain shape of steep the second spacer 30 after removed the first spacer. Using the gate electrode structure and second spacer 30 as a mask proceeding heavy doping and metallization process.

[0029] The above-disclosed details of embodiment can provide a steep spacer method. Deposited dual conformal layer for two step etching respectively. We can obtain a steep spacer but without complicating the process. The process only increase an additional step of conformal poly film deposition and etching and obtain a steep spacer. For next step proceed avoid bridge the source and drain with gate in the salicide process, and keep off short of the source and drain with gate happen.

[0030] Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims. 

What is claimed is:
 1. A method for forming a steep spacer in a metal-oxide-semiconductor device, said method comprising: providing a semiconductor substrate, and a gate electrode on the substrate; depositing a dielectric layer on said gate electrode and said substrate; depositing a dummy layer on said dielectric layer; etching said dummy layer to form a first spacer on sidewall of the dielectric layer; etching said dielectric layer to form a second spacer on sidewall of the gate electrode by using the first spacer as a mask; and removing said first spacer.
 2. The method according to claim 1, wherein said gate electrode structure comprises a silicon oxide layer and a polysilicon layer thereon.
 3. The method according to claim 1, wherein said dielectric layer comprises TEOS.
 4. The method according to claim 1, wherein said dielectric layer comprises silicone nitride.
 5. The method according to claim 3, wherein said dielectric layer is formed by chemical vapor deposition process.
 6. The method according to claim 4, wherein said dielectric layer is formed by low pressure chemical vapor deposition method.
 7. The method according to claim 1, wherein said dummy layer comprises polysilicon.
 8. The method according to claim 1, wherein said dummy layer comprises silicon nitride.
 9. The method according to claim 1, wherein said dielectric layer relative to dummy layer must have different etching selectivity.
 10. The method according to claim 7, wherein said dummy layer is deposited by low pressure chemical vapor deposition method.
 11. The method according to claim 1, wherein said method of etching dummy layer is by anisotropic-etched.
 12. The method according to claim 1, wherein said method of etching dielectric layer is by anisotropic-etched.
 13. A method for forming a steep spacer in a metal-oxide-semiconductor device, said method comprising: providing a semiconductor substrate, two field oxidation regions on said substrate, and a gate electrode structure on the substrate; depositing a dielectric layer on said gate electrode and said substrate; depositing a polysilicon layer on said conformal dielectric layer; etching said polysilicon layer to form a first spacer on sidewall of the dielectric layer; etching said dielectric layer to form a second spacer on sidewall of the gate electrode by using the first spacer as a mask; and removing said first spacer.
 14. The method according to claim 13, wherein said gate electrode structure comprises a silicon oxide layer and a polysilicon layer thereon.
 15. The method according to claim 13, wherein said dielectric layer comprises TEOS.
 16. The method according to claim 13, wherein said dielectric layer comprises silicone nitride.
 17. The method according to claim 15, wherein said dielectric layer is formed by chemical vapor deposition process.
 18. The method according to claim 16, wherein said dielectric layer is formed by low pressure chemical vapor deposition method.
 19. The method according to claim 13, wherein said polysilicon layer is deposited by low pressure chemical vapor deposition method.
 20. The method according to claim 13, wherein said method of etching polysilicon is by anisotropic-etched.
 21. The method according to claim 13, wherein said method of etching dielectric layer is by anisotropic-etched.
 22. A method for forming a steep spacer in a metal-oxide-semiconductor device, said method comprising: providing a semiconductor substrate, two field oxidation regions on said substrate, and a gate electrode structure on the substrate; depositing a silicon oxide layer on said gate electrode and said substrate; depositing a polysilicon layer on said dielectric layer etching said polysilicon layer to form a first spacer on sidewall of the silicon oxide layer; etching said silicon oxide to form a second spacer on sidewall of the gate electrode by using the first spacer as a mask; and removing said first spacer.
 23. The method according to claim 22, wherein said gate electrode structure comprises a silicon oxide layer and a polysilicon layer thereon. 